1. Field of the Invention
The present invention relates to a decoder and a decoding system, more particularly, to a decoding start controller for controlling timing at which the decoder and the decoding system commences decoding operation.
2. Description of the Related Art
MPEG (Moving Picture Experts Group) is already known as a standardized image encoding technique of compressing primarily moving picture data.
An LSI of an MPEG decoder determines decoding timing of each picture by comparing a value called VBV occupancy with the amount of bit-stream data stored in a bit-stream buffer. The value of VBV occupancy is determined by a vbv.sub.-- delay signal which defines the decoding timing of the decoder. In short, the value of VBV occupancy obtained for each picture is compared with the amount of data stored in the bit-stream buffer. The decoding of the bit-stream data in commenced if the amount of the data stored in the bit-stream buffer is equal to or greater than the value of VBV occupancy.
In the case of the MPEG decoder's LSI, a portion of the bit-stream data may be stored in an internal local buffer within the LSI. As a result, the data stored in the bit-stream buffer is reduced in the amount corresponding to the amount of the data stored in the internal local buffer, which makes it impossible to carry out appropriate decoding of the bit-stream data.
More specifically, because the amount of the data stored in the bit-stream buffer becomes smaller than the occupancy value by the previously-described reduction, decoding of a picture, particularly, decoding of the picture at the end of the sequence, cannot be commenced in spite of the fact that a picture at the end of a certain sequence has already been sent to the bit-stream buffer. Further, even in a case where extremely short bit-stream data enters the MPEG decoder in place of the final picture, the amount of the data stored in the bit-stream buffer becomes smaller than the value of VBV of occupancy by the previously-described reduction, which in turn makes it impossible to commence decoding of the bit-stream data.